1. Field of the Invention
The invention relates to electrical fault detection in electrical distribution systems (EDS) by detection and location of radio frequency (RF) emissions generated by the fault. More particularly the invention relates to self-learning radio frequency electrical fault monitor (EFM) systems and methods, having time synchronized distributed radio frequency monitors, wherein the monitoring system is trained to characterize and/or locate electrical faults based on operating state (OS) patterns learned from transmission of test signals generated within the distributions system. During operation, radio frequency emissions from the EDS are evaluated by multiple radio frequency monitors (RFM) as safe operation (SO) or potential electrical faults by accessing a base of stored knowledge concerning fault emission characteristics and/or synchronized time of arrival at each monitor. During evaluation the EFM system establishes one or more levels of confidence factors whether the monitored RF emission characteristics are indicative of electrical distribution system safe operation (SO) condition or an electrical fault its likely location within the EDS. Information in the base of stored knowledge is updated to include new operating states (OS) of the electrical distribution system. Confidence level associations, location of new radio frequency emission patterns and whether those patterns are indicative of safe operating (SO) conditions or electrical faults are stored in the base of stored knowledge.
2. Description of the Prior Art
Electrical conductors produce an electric field with the application of an electrical current. The electrical field profile can be affected by a variety of characteristics of the conductor. One characteristic that can affect the field is cracking in the conductor causing small electrical fault arcs to jump across the crack. Additionally variations in the field may also be caused by imperfections in the insulation that can allow partial electrical fault discharges consisting of very small mini-arcs on the surface of the insulation. An electrical fault arc produces a burst of broad spectrum radio frequency energy as the arc is made and again as it is broken. This applies to various types and severity of electrical fault partial discharge, discharges across bearing oil films due to shaft grounding or pedestal insulation problems, cracks in conductors, or any other kind of arcing. The signature characteristics of the RF emission will be different depending on the source.
Currently, there are several commercially available devices that monitor RF emission activity, specifically for power plant electrical generators. Partial discharge detectors monitor RF activity on the main conductors that carry electricity away from the generator (phase buses) and are typically located between the generator and the main transformer within the power plant electrical distribution system (EDS). They can consist of single sensors or multiple sensors on each phase. The use of multiple sensors can determine if an RF pulse is emanating from the generator or outside the generator by determining the direction the pulse is traveling. An existing known radio frequency monitor (RFM) available from Siemens Energy Inc., detects RF activity at a single point on the generator neutral ground. This approach is lower cost than others are, and will detect electrical fault and other RF activity from other pieces of electrical equipment in the power plant electrical distribution system (EDS), because all the equipment is typically tied to a common EDS ground or earthed phase at some plant location. However, the RFM does not determine the location of the equipment that is causing the RF emission activity: only its existence. Various manual tests and inspections must be made to locate specifically the source of the RF emission anomaly. The fault locating Utility customers find the process cumbersome and do not want the additional burden of finding the source of the problem. Typical plant maintenance practice indicates that the source of such problems become known eventually, usually when the electrical equipment in the EDS fails.
RFM's and other detection systems, such as partial discharge monitors, utilize either bus couplers or other means of voltage isolation so they can directly measure voltage waveforms of power plant equipment. The RFM output is typically observed as a series of RF spikes with quieter periods of lesser activity in between.
Existing electrical fault detection systems and methods do not efficiently isolate location of RF emissions in power plant electrical distribution systems. Those systems do not efficiently characterize whether an RF emission is an indicia of an existing or incipient electrical fault or whether the RF emission is merely part of an EDS operating state that does not negatively impact its safe operation (SO). If the latter, the detected RF emission OS can be discounted as a SO that is acceptable for power plant EDS.